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| author | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2006-12-25 03:06:05 +0000 |
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| committer | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2006-12-25 03:06:05 +0000 |
| commit | 1017cbebe5d5edd859e0fddad0a8600f509f4821 (patch) | |
| tree | 78bdf336648566f7a7d55f42837357dea3dd674c /pambackground.html | |
| parent | 16f2ac126651015a376eba864a3a35f738b0b25a (diff) | |
| download | netpbm-mirror-1017cbebe5d5edd859e0fddad0a8600f509f4821.tar.gz netpbm-mirror-1017cbebe5d5edd859e0fddad0a8600f509f4821.tar.xz netpbm-mirror-1017cbebe5d5edd859e0fddad0a8600f509f4821.zip | |
Place user guide into Subversion repository
git-svn-id: http://svn.code.sf.net/p/netpbm/code/userguide@181 9d0c8265-081b-0410-96cb-a4ca84ce46f8
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| -rw-r--r-- | pambackground.html | 128 |
1 files changed, 128 insertions, 0 deletions
diff --git a/pambackground.html b/pambackground.html new file mode 100644 index 00000000..0da0ef40 --- /dev/null +++ b/pambackground.html @@ -0,0 +1,128 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN"> +<HTML><HEAD><TITLE>Pambackground User Manual</TITLE></HEAD> +<BODY> +<H1>pambackground</H1> +Updated: 24 December 2006 +<BR> +<A HREF="#index">Table Of Contents</A> + +<H2>NAME</H2> + +pambackground - create a mask of the background area of an image + +<H2 id="synopsis">SYNOPSIS</H2> + +<B>pambackground</B> + +[<I>netpbmfile</I> + +[<b>-verbose=</b>] + +<p>Minimum unique abbreviation of option is acceptable. You may use double +hyphens instead of single hyphen to denote options. You may use white +space in place of the equals sign to separate an option name from its value. + + +<H2 id="description">DESCRIPTION</H2> + +<p>This program is part of <a href="index.html">Netpbm</a>. + +<p><b>pambackground</b> reads a PNM or PAM image as input. +It generates as output a PAM image that identifies the background area +of the image (a mask). + +<p>To identify the background, <b>pambackground</b> assumes the image +is a foreground image, smaller than the total image size, placed over +a single-color background. It assumes that foreground image is solid +-- it does not have holes through which the background can be seen. +So in specific, <b>pambackground</b> first identifies the background +color, then finds all contiguous pixels of that color in regions +touching any edge of the image. Think of it as starting at each of +the four edges and moving inward as far as possible until it hits +pixels of another color (the foreground image). + +<p><b>pambackground</b> identifies the background color as follows: +If any 3 corners of the image are the same color, that's the background +color. If not, but 2 corners are the same color, the background color +is the color of a pair of identically colored corners in this priority +order: top, right, left, bottom. If no two corners have the same color, +the background color is the color of the upper left corner. + +<p>In a typical photograph, the area that you would consider the +background is many shades of a color, so to <b>pambackground</b> it is +multiple colors and <b>pambackground</b> will not meaningfully +identify the background of your image. To use <b>pambackground</b> in +this case, you might use <b>ppmchange</b> to change all similar colors +to a single one first. For example, if the photograph is a building +against a blue sky, where nothing remotely sky-blue appears in the +building, you could use <b>ppmchange</b> to change all pixels within +20% of "SkyBlue" to SkyBlue, then run <b>pambackground</b> +on it. + +<p>As currently implemented, <b>pambackground</b> does not really +do what is promised above. It can't see places where the background +appears in the middle of a row (think of the sky between two buildings). +It will take a considerably more sophisticated algorithm to fix that; +feel free to write the code and submit it for inclusion in Netpbm. + +<p>The PAM that <b>pambackground</b> creates has a single plane, with +a maxval of 1. The sample value 1 means background; 0 means +foreground. There is no tuple type. Some older programs (but none +that are part of Netpbm) don't know what a PAM is and expect a mask to +be in the form of a PGM or PBM image. To convert +<b>pambackground</b>'s output to PBM, use <b>pamtopnm -assume</b>. To +convert to PGM, use <b>pgmtopgm</b>. + +<P><I>netpbmfile</I> is the file specification of the input file, or +<B>-</B> to indicate Standard Input. The default is Standard Input. + +<p>A common use for a background mask is with <b>pamcomp</b>. You +could replace the entire background (or foreground) of your +image with something else. + +<p>Another common use is to make an image with the background +transparent (in some image format that has a concept of transparency; +not Netpbm formats) so that image can be overlaid onto another image +later. Netpbm's converters to image formats that have transparency +(e.g. PNG) let you use the mask that <b>pambackground</b> generates +to identify the transparent areas for the output. + +<p>To simply make a mask of all the areas of a specified color, use +<b>ppmcolormask</b>. If you have a unique background color (one that +doesn't occur in the foreground) and know what it is, this can create +a background mask in cases that <b>pambackground</b> cannot: where there +are see-through holes in the foreground image. + +<H2 id="options">OPTIONS</H2> + +<dl> + +<dt><b>-verbose</b> + +<dd>Tell interesting facts about the process. + +</dl> + +<H2 id="seealso">SEE ALSO</H2> + +<B><A HREF="ppmcolormask.html">ppmcolormask</A></B>, +<B><A HREF="pamcomp.html">pamcomp</A></B>, +<B><A HREF="pamtopnm.html">pamtopnm</A></B>, +<B><A HREF="pgmtopgm.html">pgmtopgm</A></B>, +<B><A HREF="pnm.html">pnm</A></B>, +<B><A HREF="pam.html">pam</A></B>, + +<h2 id="history">HISTORY</h2> + +<P><B>pambackground</B> was new in Netpbm 10.37 (December 2006). + +<HR> +<H2 id="index">Table Of Contents</H2> +<UL> +<LI><A HREF="#synopsis">SYNOPSIS</A> +<LI><A HREF="#description">DESCRIPTION</A> +<LI><A HREF="#options">OPTIONS</A> +<LI><A HREF="#seealso">SEE ALSO</A> +</UL> +</BODY> +</HTML> |